1. Field of the Invention
The subject invention relates to a mount assembly for a vehicle having a frame and a vehicle body wherein the mount assembly isolates various movements between the frame and vehicle body.
2. Description of the Related Art
Mount assemblies for vehicles are well known in the art. Examples of such assemblies are shown in U.S. Pat. Nos. 5,743,509 and 6,416,102. Each of these assemblies includes a support structure that engages with the frame and a carrier mounted to a vehicle body. The carrier is coupled to the support structure through one or more insulators. The insulators are typically formed of an elastomeric material such as rubber or polyurethane.
One important factor in the development of mount assemblies relates to the rate of elasticity, also known as a spring rate, of the insulators. The insulators can have a relatively soft spring rate, which is preferred for isolating vibrational motion. Vibrational motion is generally associated with lower amplitudes and higher frequencies, such as when a vehicle travels over typical undulations of a road surface. It is desirable to have the insulators operate at lower or softer spring rate to allow for improved isolation and cushioning of the vibrations of the frame relative to the vehicle body.
On the other hand, the insulators can have relatively stiff or hard spring rates, which is preferred for controlling translational motion. Translational motion is typically associated with high amplitude, lower frequency impacts such as the occasional large impact when a vehicle passes over a pothole. The impacts cause a maximum displacement of the frame relative to the vehicle body.
The prior art rubber materials are such that the effective spring rate is relatively linear with the load increasing relative to the displacement of the insulator. The above trade off and linear spring rate resulted in an insulator having a soft spring rate or a stiff spring rate, but not both. This resulted in a vehicle ride characteristic that was not ideal for isolating both vibrational and translational motion associated with the movements of the frame.
The trade off in material versus spring rate has resulted in many mount assemblies utilizing materials with non-linear spring rates, such as polyurethane elastomers, which include microcellular polyurethane (MPU). Polyurethane elastomers are such that they do not have a linear spring rate and therefore can offer an insulator material capable of isolating a variety of movements of the frame to provide improved ride characteristics of the vehicle. In particular, the MPU material offers an initial low spring rate to isolate the vibrational force and additionally, as the MPU material compresses, the spring rate stiffens. This characteristic of MPU is an improvement over rubber materials. However, the prior art uses of polyurethane elastomers have additional concerns such as forming the insulator into multidimensional shapes and positioning the insulator in the mount assembly. The prior art mounts utilizing MPU are typically a simple cylindrical designs. This cylindrical shape provides limited capability of the mount to isolate lateral forces associated with frame movement.
Accordingly, it would be desirable to develop an insulator utilizing a polyurethane elastomer, such as microcellular polyurethane, formed in a shape and positioned within a mount assembly to interact with both horizontal and vertical surfaces to isolate both lateral and vertical forces associated with movements of a frame relative to a vehicle body.